Structural Modulation Of Ru-Based Materials For CO₂ Methanation

CO₂ hydrogenation is an effective way to address the problem of high global CO ₂concentration,and this advantage of selective hydrogenation of CO₂ to produce value-added chemicals has attracted much attention to this reaction.CO₂ methanation is a relatively mild process that is of great interest because of its critical importance in the carbon recycling process.In order to improve the utilization value of loaded Ru-based catalysts and further broaden their applications in CO₂ hydrogenation,this paper addresses the activity enhancement strategy and selectivity regulation strategy in CO₂ methanation process,and structural modulation of Ru-based catalysts with g-C₃N₄ and Ti O₂ as carriers,respectively,to achieve efficient enhancement of CO₂ conversion and selectivity control.The relationship between structure and catalytic performance was also further explored,and the mechanism of CO₂ hydrogenation reaction on the surface of Ru-based catalysts was analyzed with the help of in situ DRIFTS technology,providing insights into CO₂ hydrogenation.The main contents are:（1）To address the problem of how to increase the catalyst reactivity,a series of cyano-modified g-C₃N₄ were prepared by thermal polymerization and loaded with metal Ru（Ru/CN-10）by conventional impregnation.It was found that the catalytic activity was increased by 14times after the cyano modification at 250℃,and the methane selectivity was increased to99.5%,and the efficient conversion of CO₂ and higher CH₄ selectivity on g-C₃N₄ materials were achieved at low temperature.By characterization tests,the enhanced catalytic performance can be attributed to the fact that cyano increases the moderately basic sites of the material,promoting the activation of CO₂ toward the direction favorable to methanation.At the same time,the presence of cyano leads to the formation of electron-rich Ru,which promotes the activation of hydrogen.Kinetic studies demonstrate that the activation energy increases after catalyst modification.In situ DRIFTS analysis demonstrated that the combined effect of Ru and cyano promoted the adsorption of CO*material on the catalytic surface,and CO₂ was further hydrogenated to synthesize methane mainly along HCOO*over Ru/CN-10 catalyst,while the pristine catalyst passed through COOH*intermediates with a pathway of reverse water-gas conversion（RWGS）and a stepwise combination of CO-hydrogenation pathways.（2）For the selective modulation problem,a series of Ru/Ti O₂ catalysts modified by different anions were prepared by the conventional impregnation method,and the effect of by different anions on Ru/Ti O₂catalysts in CO₂ hydrogenation was investigated.Interestingly,Ru/Ti O₂-Cl,Ru/Ti O₂-NO₃ and Ru/Ti O₂-SO₄ catalysts showed poor catalytic performance for CO₂ hydrogenation,but high selectivity of CO products could be obtained.However,when Ru/Ti O₂-OH and Ru/Ti O₂-CO₃ were used as catalysts,high CO₂ conversion and highly selective CH₄ products could be obtained.XPS results showed that the anions on the surface of Ru/Ti O₂ catalysts strongly interacted with Ru metal sites.DFIRTS and CO-TPD characterization demonstrated that the Ru/Ti O₂-M catalysts on on CO₂*and H*to generate COOH*intermediates,the whole hydrogenation reaction follows the CO pathway,with the difference that the addition of OH^-and CO₃^2-enhances the stable adsorption of surface-bridged CO*,which implies that the anions on the Ru/Ti O₂ catalyst surface affect the adsorption of CO intermediates on Ru metal sites,resulting in the difference of CO₂ hydrogenation products.